MOSFET voltage booster heat and protection

Thread Starter

Je514

Joined Oct 13, 2021
3
I have an IRF640 N-channel MOSFET that has no protection on the circuit, and heats up my heatsink very fast. I know I need a Zener diode to "protect" the MOSFET, but is there anything else I need, and where do I put it? CLARIFICATION: the circuit does work, but it is killing the mosfet, it heats up a 1/2” x 2” x 2” aluminum heat sink to 104 F(40 Celsius) in 30 seconds. I don’t understand what I need to protect and improve the circuit

Wiring diagram below:
Copy of Screenshot 2021-10-14 9.53.01 AM.png
 

LowQCab

Joined Nov 6, 2012
1,308
The FET needs to be either "On" or "Off",
anything in between is going to generate lots of Heat.
That's why there are Chips for controlling Gate-Switching.

This is not a "Flyback" SMPS, it's a crude Oscillator.

You need a proper "Boost-Converter" Chip, and supporting parts.
.
.
.
 

Thread Starter

Je514

Joined Oct 13, 2021
3
The FET needs to be either "On" or "Off",
anything in between is going to generate lots of Heat.
That's why there are Chips for controlling Gate-Switching.

This is not a "Flyback" SMPS, it's a crude Oscillator.

You need a proper "Boost-Converter" Chip, and supporting parts.
.
.
.
Ah, and what type of chip would I need? Something like a 555 timer?
 

LowQCab

Joined Nov 6, 2012
1,308
A 555-Timer would not provide any Voltage-Regulation.

All of the specific details of what You are trying to accomplish, and why, are needed,
as well as the type of construction, ( I'm assuming that this is not an SMD Project ).
.
.
.
 

MisterBill2

Joined Jan 23, 2018
9,792
For starters, certainly to avoid a lot of heat, the switching device MUST be either cutoff or completely switched on, and the circuit shown is not able to do either.
Read the specifications for the FET and note the gate to source voltage to assure complete saturated switching at whatever current is passing through the transformer winding.
This circuit looks a lot like the "Tickle Stick" circuit published in some magazine in 1964. I came across it recently in a collection of old circuits. That version used a big germanium bipolar transistor and ran off a single "D" cell.
 

Thread Starter

Je514

Joined Oct 13, 2021
3
For starters, certainly to avoid a lot of heat, the switching device MUST be either cutoff or completely switched on, and the circuit shown is not able to do either.
Read the specifications for the FET and note the gate to source voltage to assure complete saturated switching at whatever current is passing through the transformer winding.
This circuit looks a lot like the "Tickle Stick" circuit published in some magazine in 1964. I came across it recently in a collection of old circuits. That version used a big germanium bipolar transistor and ran off a single "D" cell.
Ah, I think this circuit is called a “Hartley oscillator”, but anyways, how would I switch it completely on and off? Would a arduino work? Or is there something simpler and more compact?
 

MisterBill2

Joined Jan 23, 2018
9,792
I am not aware of SIMPLE FET circuits that produce a sqyare wave. So a suitable driver is needed. Others have suggested that, they can provide part numbers and circuits.
 

LowQCab

Joined Nov 6, 2012
1,308
Ah, I think this circuit is called a “Hartley oscillator”, but anyways, how would I switch it completely on and off? Would a arduino work? Or is there something simpler and more compact?
.
It's called a "Boost-Converter" Chip.
Most of these Chips can be used in a variety of different "Converter" Topologies.
.
.
.
 

MisterBill2

Joined Jan 23, 2018
9,792
The gate voltage requirements for driving a FET in a switching mode are rather demanding and need to be taken seriously in the design. Using one of the many driver ICs will certainly be the way to go.
 

Ian0

Joined Aug 7, 2020
3,754
Another possibility is that the circuit IS ACTUALLY WORKING, but without any load connected the output voltage keeps on increasing until something breaks down. The MOSFET will avalanche (many of them are designed to avalanche without failing) and dissipate the power.
 

MisterBill2

Joined Jan 23, 2018
9,792
Another possibility is that the circuit IS ACTUALLY WORKING, but without any load connected the output voltage keeps on increasing until something breaks down. The MOSFET will avalanche (many of them are designed to avalanche without failing) and dissipate the power.
When you evaluate the circuit it is clear that the transistor is operating in the linear mode constantly. So it is going to get hot no matter what.
 
Top